Field of the Invention
The present disclosure relates to toners, toner stored units, and image forming apparatuses.
Description of the Related Art
In image forming apparatuses, such as an electrophotographic device, and an electrostatic recording device, a toner is deposited on an electrostatic latent image formed on a photoconductor to form a toner image, and the toner image is transferred to a recording medium, followed by heating to fix the toner image.
When a full-color image is formed, moreover, fixing is performed by heating, after overlapping toner images of each of 4 colors, typically using toners of 4 colors, black, yellow, magenta, and cyan. As the technology of electrophotography develops, the aforementioned toner is required to have low temperature fixing ability, and storage stability.
To meet the aforementioned demands, low temperature fixing ability of a toner is achieved with low viscosity or low glass transition temperature of a binder resin for use. However, such a toner has problems, such as reduction in blocking resistance of a toner, reduction in storage stability of a toner in high temperature high humidity environment, and low charge due to a change caused on surfaces of toner particles.
To solve the aforementioned problems, recently proposed has been an invention associated with a technique using a crystalline resin and an amorphous resin as a binder resin (see Japanese Patent Application Laid-Open (JP-A) Nos. 2005-234046 and 2012-108462). It is disclosed that mainly crystalline polyester is used as a crystalline resin in a toner.
In the aforementioned literatures, low temperature fixing ability of a toner is improved by making crystalline polyester compatible with heat history during fixing, and it is attempted to improve blocking resistance through a selection of a release agent for use, or an adjustment of an amount of a release agent. However, storage stability of a toner in high temperature high humidity environments has not been concerned therein.
Both of the aforementioned literatures mention about an improvement of blocking resistance, and storage stability against high temperature, but storage stability of a toner associated with high humidity has not been sufficiently studied therein. Meanwhile, disclosed is a technique where hydrophobicity of a toner is enhanced by controlling a hydroxyl value of a binder resin for use to overcome reduction in storage stability of the toner in high temperature high humidity environment, or low charge due to a change caused on surfaces of toner particles (see JP-A No. 2004-295110 and WO2010/143385).
In these literatures, there are descriptions that blocking resistance of a toner is improved, an environment hardly affect the toner during image formation, and a toner image of high image quality can be formed on various types of paper. However, the technology disclosed therein does not aim to improve low temperature fixing ability or storage stability of the toner, or to prevent surface changes. Accordingly, there has been a need for a toner, whose low temperature fixing ability or storage stability is improved, and surface changes of which are prevented.
Moreover, there is an attempt to achieve low temperature fixing ability and heat resistant storage stability, and to prevent surface changes after left to stand in a high temperature high humidity environment, through a control method using sol-gel silica of external additives (see JP-A No. 2014-163949), but an improvement has not been achieved with structures of toner base particles.